There's a "mask" with pictures covering my desktop

Some kind of screen/mask one day completely covered my desktop.. it's like a file or something because when I click properties.. it brings it up as if properties of a file instead of giving me the usual options for desktop/screensaver/windows themes/etc.

When I turn off my computer.. it shuts down like a regular program/file would and I can see my actual desktop for a brief 5 seconds before my computer shuts down.